Crude, lymphokine-active cultural supernatants were obtained from: 1., isolated liver granulomas of S. mansoni infected mice 2., isolated lung granulomas obtained from methylated bovine serum albumin-adjuvant sensitized and antigen-coupled bead injected mice and 3., Concanavalin A stimulated normal mouse spleen cells. Crude supernatants of hypersensitivity granulomas were concentrated, dialyzed and tested for macrophage migration inhibition (MMI) activity using syngeneic peritoneal macrophages. MIF active substances were separated by Amicon membranes into 3 fractions; No. 1 (greater than 100.000 M.W) No. 2 (50-100.000 M.W) and No. 3 (less than 50.000 M.W). MIF activity was found in Fractions 1 and 2 of both liver and lung granulomas. Fraction 2 of the mitogen-stimulated spleen cell supernatant showed similar activity. MMI activity in Fraction 2 of the liver granulomas was destroyed by heating at 56 degrees centigrade for 30 min. Treatment with neuraminidase enzyme had no effect. Disc gel electrophoresis of the fraction revealed 5 well-isolated bands. Further purification processes are now in progress.